Natural Water and Chemical Budgets for a Small Precambrian Lake Basin in Central Canada

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Abstract
Results of a 4-yr study of the hydrology of the Rawson Lake watershed, as well as the chemistry of precipitation, streamflow, and the lake are presented. Inputs of water and most chemicals varied by as much as 2 times from one year to the next, illustrating that several years’ data are necessary to determine accurately average nutrient inputs and losses from an ecosystem. Precipitation appeared to be almost the sole source of P and N to lake and terrestrial ecosystems, although N2 fixation cannot be dismissed in the latter case. Significant proportions of Ca, Mg, Na, K, Cl, and SO4 were supplied directly from precipitation. The lake also received substantial quantities of these elements as well as silicon, from weathering of terrestrial geological materials. Although far from any major industrial sources of SO2, the pH of precipitation averaged < 5 for the years studied. Both terrestrial and lake systems retained a high proportion of entering P and N, and smaller proportions of other nutrients. Interpretation of relative retentions of nutrients revealed that the terrestrial ecosystem has well-balanced P and N supplies, while the lake was P limited. Rates of loss of chemicals from the terrestrial watershed of Rawson Lake are comparable to other sites in the Precambrian Shield, but lower than values from other geological settings.

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